This invention relates generally to a hand held, patient actuated controller which commands an automatic implantable defibrillator to record electrocardiogram (ECG) signals representing the patient's heart physiology recently detected over a predetermined time period.
Automatic defibrillators are implanted within patients to monitor the electrical activity of the heart of the patient. The automatic defibrillator continuously monitors the heart's activity and determines whether certain arrhythmic events occur, e.g., ventricular fibrillation, ventricular tachycardia, atrial fibrillation, asystole, etc. Upon detecting one of the cardiac events, the automatic defibrillator provides appropriate cardioversion therapy via electrical pacing pulses to the heart and/or a countershock to the heart as programmably established in the defibrillator by the patient's physician. The implantable automatic defibrillator includes a microprocessor and associated digital components such as random access memories (RAMs) and read only memories (ROMs) to carry out these functions.
U.S. Pat. No. 4,407,288 by Langer et al. discloses a programmable, microprocessor based implantable defibrillator; the patent is incorporated herein by reference thereto. The patent discloses the use of two microprocessors, one high speed processor and another low power, low speed processor and discloses a scheme for recording ECG data. To determine whether a predetermined event has occurred, the ECG data is loaded into a precursor memory via a direct memory access (DMA) operation. The low power microprocessor monitors the ECG data in the precursor memory and a dedicated cardiac state evaluation circuit detects the presence of an event, such as an arrhythmia, and then generates appropriate signals directed towards the low power microprocessor. In the absence of signals indicating the occurrence of a predetermined event, the high powered microprocessor is "asleep." When an event is detected, the ECG data in the precursor memory is automatically "frozen" therein and the high speed microprocessor is "awakened" to pass programmable cardioversion commands to other circuitry in the automatic defibrillator. A mechanism is also described in the patent for outputting the ECG data from the precursor memory.
U S. Pat. No. 4,295,474 by Fischell discloses a recorder for an automatic implantable defibrillator; the patent is incorporated herein by reference thereto. The most recently detected ECG data is stored or recorded in a precusor section of a RAM. If an event occurs, a second continuous recording of ECG data is started in the larger portion of the memory; however, further recording or writing of ECG data into the precusor section or the recorded portions of the RAM is inhibited until the contents of the RAM is read out via a telemetry communication link to a physician's console. The physician analyzes the ECG data stored in the precusor memory section immediately preceding the defibrillation activity and stored in the recorded portions of the RAM during the defibrillation episode. Even if no fibrillation episodes (detected cardiac events) have occurred since the patient's last visit to the physician, the physician may place a control command coil or magnet over the implantable defibrillator to instruct the defibrillator to record approximately 70 seconds of current patient ECG data and then immediately transmit that ECG data to the physician's console via a telemetry communication link.
U.S. Pat. No. 4,223,678 by Langer et al. discloses an arrhythmia recorder as part of an implantable defibrillator. In this patent, the ECG data is converted from analog into digital and stored in a first in, first out (FIFO) auxiliary memory. When a fibrillation event is detected, the auxiliary memory is disabled such that no further ECG data is recorded therein and a main memory is actuated to record ECG data during the defibrillation episode. Thereafter, no further ECG data is recorded in the auxiliary memory and the main memory until the physician sends an appropriate command, via a command console, to transmit the ECG data from the auxiliary memory and the main memory to the console by way of a telemetry communication link.
The above noted patents do not discuss a hand held patient record controller which is actuable by the patient and which commands the implantable defibrillator to record the current ECG data.
Because there is a need to establish electronic parameters in the arrhythmia or event detector to properly detect varying degrees of cardiac activity, particularly when microprocessor based defibrillators are capable of distinguishing numerous types of events, it is desirous to record the ECG signals since the detector parameters vary slightly from patient to patient. Also, the defibrillators now provide a plurality of pacing modes to be delivered to the heart dependent upon the type of event. The pacing mode programmed by the physician is dependent upon the previously gathered ECG data by the physician. The greater number of treatment modes generally requires greater number of parameter settings because the physician can establish parameters for the arrhythmia detector and values for the identification of the type of event by the microprocessor which triggers the delivery of a prescribed treatment to the heart. By increasing the modes of treatment, the establishment of parameters to trigger a particular mode is further complicated.
The patient is in a good position to identify the onset of any particular cardiac event, e.g., an arrhythmia. If the parameters in the automatic implantable defibrillator are properly set, the defibrillator will respond, notwithstanding the patient's concern, with the appropriate mode of treatment and record the ECG data. However, if the parameters have been set incorrectly, the defibrillator will not recognize the arrhythmia and hence will not apply any treatment but further will not record the ECG data. In the absence of an ECG recording, the defibrillator cannot be "fine tuned" for a patient's particular requirements. Therefore, a simple, hand held, patient ECG record controller allows the patient to command the implantable defibrillator to record a predetermined amount of recently monitored ECG data whenever the patient feels the onset of a cardiac event.